The present invention relates to a single optical fiber ferrule and to a method for terminating the ferrule to a fiber optic cable.
U.S. Pat. No. 4,087,155 to Deacon, assigned to the assignee of the present application, discloses a connector for coupling a pair of single optical fibers which provides precise lateral alignment between the fibers. Each contact or ferrule of the connector utilizes three spheres of equal diameter defining a tricuspid interstitial space therebetween into which the end of a fiber is mounted. The spheres are arranged in closely adjacent, but not necessarily engaging relationship in each ferrule. The centers of the spheres of each ferrule lie in a common plane normal to the axial length of the optical fiber. The spheres are dimensioned, to a close tolerance, to closely confine the fiber in the interstitial space. The spheres of one of the ferrules abuts under an axial compression force against those of the other ferrule so that the spheres nest with respect to each other, whereby the optical fiber in the space of said one ferrule is brought into close lateral alignment with that of the mating ferrule.
In one embodiment disclosed in the Deacon patent, the spheres are dimensioned relative to the optical fiber so that the spheres all engage each other, but do not engage the fiber, whereby the fiber has a slightly loose fit in the interstitial space between the spheres. This arrangement is convenient since the fiber can be inserted into the interstitial space without an interference fit. However, because the fiber is loose in the space, light transmission losses may occur between mating ferrules. The Deacon patent discloses a second embodiment in which the spheres are dimensioned relative to the fiber so that they all engage the fiber, but do not engage each other. In this case, there is an interference fit between the fiber and the spheres, making insertion of the fiber between the spheres more difficult, but more precise lateral alignment of the fibers in two mating ferrules may be achieved.
Copending application of R. L. McCartney, Ser. No. 861,110 filed Dec. 16, 1977, now U.S. Pat. No. 4,158,476 entitled: "Single Optical Fiber Connector", assigned to the assignee of the present application, discloses an optical fiber ferrule utilizing alignment spheres with adjustment means which allows the spheres to spread apart to facilitate insertion of an oversized fiber therebetween. Such adjustment means comprises a collar which is mounted on the forward end of the ferrule body. A radially inwardly directed lip on the forward end of the collar retains the spheres against the front face of the body. The lip exerts a radially inwardly and rearwardly directed force against the spheres to retain and consolidate the spheres at the front of the ferrule. By moving the collar forwardly on the ferrule body, the force on the spheres is released, thereby allowing an optical fiber to be inserted into the interstitial space between the spheres even though the fiber is slightly oversized. The collar is then moved rearwardly so that the inwardly directed lip thereon urges the spheres inwardly around the fiber. Thus, the interstitial space may be adjusted to accommodate an oversized fiber, whereby the fiber is firmly mounted in the space thus minimizing light transmission losses between mating ferrules.
To maximize light transmission through a pair of mating ferrules, the fiber end faces in the ferrules must be precisely located so that they will abut when the ferrules are mated. As explained in the Deacon patent, the precise location of the end face of the fiber may be achieved by using a fourth larger sphere nested among the three spheres at the front thereof. The fiber end face, when positioned against this sphere, will be at the precise recessed location required to provide a zero gap when aligned with the fiber in a mating ferrule. The location of the fiber end face required when two ferrules are mated and the diameter of the fourth fiber positioning sphere are disclosed in the Deacon patent.
To terminate a ferrule of the aforementioned type to an optical fiber, the first step is to prepare the end face of the fiber. The end face must be perpendicular to the fiber axis optically clear. A known method for achieving such an end face is by cleaving. To cleave the fiber, it is pulled in tension and scribed with a diamond or other suitable hard material. Once the fiber is cleaved, it is threaded through the ferrule. To allow the spheres to spread, the collar on the forward end of the ferrule is loosened as previously explained. The fiber is positioned approximately even with the front of the spheres. Then the spheres are clamped lightly to the fiber by the collar. By nesting the large sphere to the front of the three spheres in the ferrule, the fiber is pushed back to its proper location. An epoxy may then be used to permanently retain the fiber in proper position in the ferrule. While this procedure is entirely satisfactory, it is time consuming and requires a relatively high degree of skill.
It is the object of the present invention to provide a novel method of terminating an optical fiber ferrule, which embodies alignment spheres, to a fiber optic cable which may be performed more rapidly and with less skill than the prior procedures, and without the requirement of a fourth fiber positioning sphere, and to provide a novel fiber optic ferrule which facilitates the implementation of such method.